1. Field of the Invention
The present invention relates to a relay variable power optical system and a microscope equipped with the optical system, and particularly, to a relay variable power optical system for forming a secondary image based on the light from a primary image in the microscope.
2. Related Background Art
As a microscope apparatus or as an inspecting or a measuring apparatus using a microscope, an apparatus is conventionally known in which the light sent from the primary image by an objective lens is re-imaged as a secondary image onto a focal plane of an eyepiece lens, an image plane of a TV camera, or the like, through a relay optical system.
If, for example, a relay system of an optical system such as a microscope is to be adapted as a zoom lens in a simple structure, it becomes difficult to maintain the relationship between an entrance pupil and an exit pupil of the relay optical system to be substantially constant while maintaining the positional relationship between the primary image and the secondary image. More specifically, when a specific lens within the relay optical system is positively moved along the direction of the optical axis in order to change an image magnification while maintaining the positional relationship between the primary image and the secondary image, the position of the exit pupil of the optical system is widely changed with the movement of this lens. For this reason, when the secondary image which is formed by the relay optical system is observed in an enlarged manner by use of an eyepiece lens or the like, the position of an eye point is changed following a change of the image magnification. As a result, a part of the observation light may be vignetted (or eclipsed) to deteriorate an observed image, or the positions of the eyes must be displaced whenever the image magnification is changed, whereby it becomes very troublesome to observe the image.
When two dichroic mirrors or the like are provided between the relay optical system and the secondary image formed by the optical system so as to form three secondary images for respective wavelengths and the images are detected by use of a TV camera of a three-tube type which has three image elements provided at the respective positions of the secondary images, if an inclination or a telecentricity of a chief ray entering into the above-mentioned two dichroic mirrors is changed due to the movement of the exit pupil of the relay optical system, wavelength separation characteristics of the two dichroic mirrors are changed, and colors become unfavorably uneven around the image photoelectrically detected.